Level 3 Chemistry (91390) 2021 - NZQA

91390

913900

3

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Level 3 Chemistry 2021

91390 Demonstrate understanding of thermochemical principles and the properties of particles and substances

Credits: Five

Achievement

Demonstrate understanding of thermochemical principles and the properties of particles and substances.

Achievement with Merit

Demonstrate in-depth understanding of thermochemical principles and the properties of particles and substances.

Achievement with Excellence

Demonstrate comprehensive understanding of thermochemical principles and the properties of particles and substances.

Check that the National Student Number (NSN) on your admission slip is the same as the number at the top of this page. You should attempt ALL the questions in this booklet. A periodic table and other reference material are provided in the Resource Booklet L3?CHEMR. If you need more room for any answer, use the extra space provided at the back of this booklet. Check that this booklet has pages 2?12 in the correct order and that none of these pages is blank. Do not write in any cross-hatched area ( ). This area may be cut off when the booklet is marked. YOU MUST HAND THIS BOOKLET TO THE SUPERVISOR AT THE END OF THE EXAMINATION.

? New Zealand Qualifications Authority, 2021. All rights reserved. No part of this publication may be reproduced by any means without the prior permission of the New Zealand Qualifications Authority.

2 QUESTION ONE (a) Complete the following table.

Symbol Sc Ga Fe3+

Electron configuration (use s, p, d notation)

(b) (i) Complete the table below. SeF4

ClF4?

Lewis structure

Name of shape

(ii) Both vapH?(SeF4) and fusH?(SeF4) are positive. Explain why vapH?(SeF4) is more positive.

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(c) Potassium nitrate, KNO3, readily dissolves in water according to the equation below: KNO3(s) K+(aq) + NO3?(aq) rH? = +34.9 kJ mol?1

(i) Justify, in terms of the entropy changes of the system and the surroundings, why the reaction is spontaneous.

(ii) When solid KNO3 dissolves in water, the temperature decreases from 21.3 ?C to 14.2 ?C.

Calculate the mass of solid KNO3 that must dissolve to cause this temperature decrease. Assume the specific heat capacity of potassium nitrate solution is 4.18 J g?1 ?C?1.

Assume the mass of the potassium nitrate solution is 135 g.

M(KNO3) = 101 g mol?1

Chemistry 91390, 2021

4 QUESTION TWO (a) Explain the difference in the atomic radii of calcium and selenium.

Calcium, Ca Selenium, Se

Atomic radius / pm 197 116

(b) Justify, with reference to the factors affecting periodic trends, why fluorine is the most electronegative element in Group 17.

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(c) (i) The equation for the reaction of ammonia, NH3, with oxygen, O2, is given below: 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)

Calculate the standard enthalpy change for this reaction, rH?, using the following data:

2NH3(g) N2(g) + 3H2(g)

rH? = +92 kJ mol?1

2H2O(g) 2H2(g) + O2(g)

rH? = +572 kJ mol?1

N2(g) + O2(g) 2NO(g)

rH? = +180 kJ mol?1

(ii) Explain why the standard enthalpy change calculated in part (i) would be more exothermic if the water was produced as a liquid.

Chemistry 91390, 2021

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